Re: [PATCH 3/4] sg: check for valid direction before starting the request

[Christoph Hellwig <hch@lst.de>]

On Fri, Feb 03, 2017 at 09:54:50AM +0100, Hannes Reinecke wrote:
> From: Johannes Thumshirn <jthumshirn@suse.de>
> 
> Check for a valid direction before starting the request, otherwise we risk
> running into an assertion in the scsi midlayer checking for vaild requests.

Good idea, but..

> +static bool sg_is_valid_direction(int dxfer_direction)
> +{
> +	switch (dxfer_direction) {
> +	case SG_DXFER_NONE:
> +	case SG_DXFER_TO_DEV:
> +	case SG_DXFER_FROM_DEV:
> +	case SG_DXFER_TO_FROM_DEV:

This isn't strictly valid as sg doesn't actually handle real bidi
commands, but we work around it.

It might be a good idea to move the warning about it from sg_write
to here and use printk_ratelimited instead of the hand-rolled
per-thread warning there.

> +	case SG_DXFER_UNKNOWN:
> +		return true;

And how valid is this one (Question to Doug I guess): for a 0-sized
transfer we should be fine, but otherwise it should probably be
rejected.